1860, from wish + bone (n.); so called from the custom of making a wish while pulling the bone in two with another person. The wishbone breaking custom dates to the early 17c., when the bone was a merrythought.

(wĭsh'bōn') The forked bone in front of the breastbone in most birds, consisting of the two collarbones partly fused together. It serves as a spring, capturing some of the energy during the downward stroke of the wings for release on the upward stroke.